Beneath the Mask: An Introduction to Theories of Personality by Christopher F. Monte and Robert N. Sollod (2003, Hardcover, Subsequent Edition)

Beneath the Mask does a great job of giving background on the most influential theorists in psychology so you not only learn their theories but are able to see why they may have come up with it from their own experiences. As a grad student in psychology, I've seen my fair share of textbooks and the background really helps fill things out.
Though fairly easy to read, it is still a psychology textbook. It assumes nothing, however, so it's great for beginners. It also gives a fairly thorough analysis of each theory, keeping it from being overly simplified.
If you are required to buy it for class or just interested in learning about psychological theories and their theorists, this is a good read/reference.

I had to purchase this book for a graduate level course. It was very difficult to understand and I felt like I was reading in circles. If you have to purchase this book for a class, I would suggest googling the different personality disorder theorist.

It's not a bad book, but there is a lot of perhaps unnecessary background information about each psychologist. I haven't read the whole thing yet, but it's been tough for me to get through. The chapters are fairly long, but there is some good information.